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// Copyright 2011 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/**
* @fileoverview Utility class to manage the mathematics behind computing an
* exponential backoff model. Given an initial backoff value and a maximum
* backoff value, every call to backoff() will double the value until maximum
* backoff value is reached.
*
*/
goog.provide('goog.math.ExponentialBackoff');
goog.require('goog.asserts');
/**
* @struct
* @constructor
*
* @param {number} initialValue The initial backoff value.
* @param {number} maxValue The maximum backoff value.
* @param {number=} opt_randomFactor When set, adds randomness to the backoff
* and decay to avoid a thundering herd problem. Should be a number between
* 0 and 1, where 0 means no randomness and 1 means a factor of 0x to 2x.
* @param {number=} opt_backoffFactor The factor to backoff by. Defaults to 2.
* Should be a number greater than 1.
* @param {number=} opt_decayFactor The factor to decay by. Defaults to 2.
* Should be a number between greater than one.
*/
goog.math.ExponentialBackoff = function(
initialValue, maxValue, opt_randomFactor, opt_backoffFactor,
opt_decayFactor) {
goog.asserts.assert(
initialValue > 0, 'Initial value must be greater than zero.');
goog.asserts.assert(
maxValue >= initialValue,
'Max value should be at least as large as initial value.');
if (goog.isDef(opt_randomFactor)) {
goog.asserts.assert(
opt_randomFactor >= 0 && opt_randomFactor <= 1,
'Randomness factor should be between 0 and 1.');
}
if (goog.isDef(opt_backoffFactor)) {
goog.asserts.assert(
opt_backoffFactor > 1, 'Backoff factor should be greater than 1');
}
if (goog.isDef(opt_decayFactor)) {
goog.asserts.assert(
opt_decayFactor >= 1, 'Decay factor should be greater than 1');
}
/**
* @type {number}
* @private
*/
this.initialValue_ = initialValue;
/**
* @type {number}
* @private
*/
this.maxValue_ = maxValue;
/**
* The current backoff value.
* @type {number}
* @private
*/
this.currValue_ = initialValue;
/**
* The current backoff value minus the random wait (if there is any).
* @type {number}
* @private
*/
this.currBaseValue_ = initialValue;
/**
* The random factor to apply to the backoff value to avoid a thundering herd
* problem. Should be a number between 0 and 1, where 0 means no randomness
* and 1 means a factor of 0x to 2x.
* @type {number}
* @private
*/
this.randomFactor_ = opt_randomFactor || 0;
/**
* Factor to backoff by.
* @type {number}
* @private
*/
this.backoffFactor_ = opt_backoffFactor || 2;
/**
* Factor to decay by.
* @type {number}
* @private
*/
this.decayFactor_ = opt_decayFactor || 2;
};
/**
* The number of backoffs that have happened.
* @type {number}
* @private
*/
goog.math.ExponentialBackoff.prototype.currBackoffCount_ = 0;
/**
* The number of decays that have happened.
* @type {number}
* @private
*/
goog.math.ExponentialBackoff.prototype.currDecayCount_ = 0;
/**
* Resets the backoff value to its initial value.
*/
goog.math.ExponentialBackoff.prototype.reset = function() {
this.currValue_ = this.initialValue_;
this.currBaseValue_ = this.initialValue_;
this.currBackoffCount_ = 0;
this.currDecayCount_ = 0;
};
/**
* @return {number} The current backoff value.
*/
goog.math.ExponentialBackoff.prototype.getValue = function() {
return this.currValue_;
};
/**
* @return {number} The number of times this class has backed off.
*/
goog.math.ExponentialBackoff.prototype.getBackoffCount = function() {
return this.currBackoffCount_;
};
/**
* @return {number} The number of times this class has decayed.
*/
goog.math.ExponentialBackoff.prototype.getDecayCount = function() {
return this.currDecayCount_;
};
/**
* Initiates a backoff.
*/
goog.math.ExponentialBackoff.prototype.backoff = function() {
// If we haven't hit the maximum value yet, keep increasing the base value.
this.currBaseValue_ =
Math.min(this.maxValue_, this.currBaseValue_ * this.backoffFactor_);
var randomWait = this.randomFactor_ ?
Math.round(
this.randomFactor_ * (Math.random() - 0.5) * 2 *
this.currBaseValue_) :
0;
this.currValue_ = Math.min(this.maxValue_, this.currBaseValue_ + randomWait);
this.currBackoffCount_++;
};
/**
* Initiates a decay.
*/
goog.math.ExponentialBackoff.prototype.decay = function() {
// If we haven't hit the initial value yet, keep decreasing the base value.
this.currBaseValue_ =
Math.max(this.initialValue_, this.currBaseValue_ / this.decayFactor_);
var randomWait = this.randomFactor_ ?
Math.round(
this.randomFactor_ * (Math.random() - 0.5) * 2 *
this.currBaseValue_) :
0;
this.currValue_ =
Math.max(this.initialValue_, this.currBaseValue_ + randomWait);
this.currDecayCount_++;
};
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